In the case of, for example, a power conversion device for a vehicle, an inverter circuit that consists of semiconductor chips for power and a heat dissipation substrate and so on is modularized. In order to keep the wiring between the semiconductor module and a driver circuit board for driving the inverter circuit to the minimum limit, the driver circuit board is mounted in proximity to the semiconductor module, and is electrically connected to the control terminals of the semiconductor module by fixing with solder or the like.
Generally, if the battery voltage is a high voltage such as 42V or greater, in the interests of safety, a controller and the driver circuit are separated by signal transmission elements such as photo-couplers or the like. Furthermore, in order to ensure insulation between the positive electrode side input and the negative electrode side input, it is necessary to guarantee that the distances between the upper and lower arms are larger than a certain value, so as to ensure insulation between them.
Moreover, since the voltage of an upper arm driver circuit portion that is connected to an upper arm power semiconductor changes from plus to minus each time the upper arm power semiconductor is switched, accordingly it is necessary to ensure good insulation between locations that are at the potential of the positive electrode and locations that are at the potential of the negative electrode. Furthermore, if it is necessary to supply a high current for driving a motor, it is necessary to ensure that the insulation is proof against fluctuations of electrical potential, because the potentials between the various phases of the lower arm driver circuit portions that are connected to the lower arm power semiconductors fluctuate along with change of the current.
As described above, the driver circuit board has circuit portions at different potentials, i.e. some portions that are connected to the controller and are at low potential, some portions that are connected to the battery and are at positive potential or negative potential, and some portions that are at output terminal potential so that they change between positive and negative potential each time switching occurs; and so, in each case, it is necessary to maintain a certain necessary distance between the various portions, and to ensure insulation between them.
For example, with the technique described in Patent Document #1, it is proposed to mount photo-couplers for signal insulation on an external portion around the driver circuit board, etc., and thereby it is anticipated that the driver circuit board can be made more compact while still ensuring insulation between the various components.
Patent Document #1: Japanese Laid-Open Patent Publication 2007-336793